Many infusion pumps are known, both with programmable control regimens and with preset or even structurally-fixed delivery characteristics. In practice, a decision to medicate a patient typically results from testing and diagnosis, and involves a decision on dosage, often together with actions to monitor the effects of medication, or the symptomatic need for further or continued medication. The target condition may be such that monitoring is necessary only at intervals of days, weeks or longer. In other cases, a medication may be administered prophylactically, before detection of a symptom, or it may be administered belatedly, when symptomatic secondary effects have been observed and the medication can, at best, limit further damage. In some circumstances, monitoring may also be required to detect the occurrence of a specific side effect or adverse reaction.
A drug delivery system typically includes an infusion pump, for example, having a housing which contains a fluid pump and a drug chamber. The pump may be implanted subdermally, with a local outlet, or with a delivery (infusion) catheter extending from the pump to an intended drug delivery site in target tissue. Thus, such a system can be partly or wholly implanted within an individual. The infusion catheter, if one is provided, is routed so as to deliver the drug to a target site within a subject. To operate the drug delivery system, the fluid pump is activated, which may be set based on expected conditions, and which regulates the duration, flow rate or other parameters of drug delivery. Once the fluid pump is activated, fluid moves along the delivery catheter toward the target site, and is released at the target site.
Certain closed-loop feedback control drug delivery systems are known and are employed for monitoring and treating disorders of the CNS. Such systems often employ sensors that detect electric activity resulting from some patho-physiological event. For example, U.S. Pat. No. 5,735,814 discloses a closed-loop system comprising multiple sensor electrodes for treating neurological diseases. This system employs electrodes which are placed in close proximity to the brain or deep within brain tissue in order to detect a secondary event such as electrical activity that is produced in response to some neurological event. The electrodes can detect the electrical activity resulting from the neurological event, e.g., the electrical activity following an ischemic event in the CNS. A signal from the monitoring system is then communicated to a control unit. The control unit will process the information and then initiate a response in order to terminate the undesirable neurological event, e.g., the release and delivery of one or more drugs from an infusion pump system.
Methods for treating neurodegenerative disorders like Parkinson's disease have been described, for example, in U.S. Pat. Nos. 5,711,315 and 6,016,449. Some methods include an infusion pump implanted within the affected individual. Along with the infusion pump, a monitoring system is also employed. Sensors placed within the brain detect aberrant electrical activity and communicate with a microprocessor which, in turn, regulates the infusion pump. Drugs housed within the infusion pump are released into certain brain areas in response to a signal sent from the microprocessor.
One concern regarding these systems is that by relying upon the detection of secondary phenomena, such as the electrical activity, rather than the primary phenomena, response time and therapeutic precision may be compromised.
Accordingly, there currently exists a need for an implantable closed-loop feedback drug delivery system which includes a monitoring system capable of directly measuring a primary biochemical parameter which underlies a particular disorder, and responding rapidly to the detected biochemical parameter with an appropriate drug treatment.